Chemistry: analytical and immunological testing – Including sample preparation – Liberation or purification of sample or separation of...
Reexamination Certificate
1999-12-03
2002-11-12
Warden, Jill (Department: 1743)
Chemistry: analytical and immunological testing
Including sample preparation
Liberation or purification of sample or separation of...
C436S174000, C422S105000, C210S121000, C210S122000
Reexamination Certificate
active
06479298
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a device and method for separating heavier and lighter fractions of a fluid sample. More particularly, this invention relates to a device and method for collecting and transporting fluid samples whereby the device and fluid sample are subjected to centrifugation in order to cause separation of the heavier fraction from the lighter fraction of the fluid sample.
2. Description of Related Art
Diagnostic tests may require separation of a patient's whole blood sample into components, such as serum or plasma, the lighter phase component, and red blood cells, the heavier phase component. Samples of whole blood are typically collected by venipuncture through a cannula or needle attached to a syringe or an evacuated collection tube. Separation of the blood into serum or plasma and red blood cells is then accomplished by rotation of the syringe or tube in a centrifuge. Such arrangements use a barrier for moving into an area adjacent the two phases of the sample being separated to maintain the components separated for subsequent examination of the individual components.
A variety of devices have been used in collection devices to divide the area between the heavier and lighter phases of a fluid sample.
The most widely used device includes thixotropic gel materials such as polyester gels in a tube. The present polyester gel serum separation tubes require special manufacturing equipment to prepare the gel and to fill the tubes. Moreover, the shelf-life of the product is limited in that overtime globules may be released from the gel mass. These globules have a specific gravity that is less than the separated serum and may float in the serum and may clog the measuring instruments, such as the instrument probes used during the clinical examination of the sample collected in the tube. Such clogging can lead to considerable downtime for the instrument to remove the clog.
No commercially available gel is completely chemically inert to all analytes. If certain drugs are present in the blood sample when it is taken, there can be an adverse chemical reaction with the gel interface.
Therefore, a need exists for a separator device that (i) is easily used to separate a blood sample; (ii) is independent of temperature during storage and shipping; (iii) is stable to radiation sterilization; (iv) employs the benefits of a thixotropic gel barrier yet avoids the many disadvantages of placing a gel in contact with the separated blood components; (v) minimizes cross contamination of the heavier and lighter phases of the sample during centrifugation; (vi) minimizes adhesion of the lower and higher density materials against the separator device; (vii) is able to move into position to form a barrier in less time than conventional methods and devices; (viii) is able to provide a clearer specimen with less cell contamination than conventional methods and devices; and (ix) can be used with standard sampling equipment.
SUMMARY OF THE INVENTION
The present invention is a method and assembly for separating a fluid sample into a higher specific gravity phase and a lower specific gravity phase. Desirably, the assembly of the present invention comprises a plurality of constituents. Preferably, the assembly comprises a container and a composite element.
Most preferably, the container is a tube and the composite element is a separator arranged to move in the tube under the action of centrifugal force in order to separate the portions of a fluid sample.
Most preferably, the tube comprises an open end, a closed end and a sidewall extending between the open end and closed end. The sidewall comprises an outer surface and an inner surface. The tube further comprises a closure disposed to fit in the open end of the tube with a resealable septum. Alternatively, both ends of the tube may be open, and both ends of the tube may be sealed by elastomeric closures. At least one of the closures of the tube may include a resealable septum.
Preferably, the separator element is releaseably positioned at the open end of the tube with the closure. Alternatively, the separator element may also be releasably positioned at the closed end of the tube.
Preferably, the closure may further include a bottom recess that extends into the tube having a plurality of inwardly extending circumferentially spaced flexible walls or a flexible full ring for holding the separator.
Preferably, the separator element comprises an overall specific gravity at a target specific gravity of &sgr;
t
. The target specific gravity is that required to separate a fluid sample into at least two phases.
Preferably, the separator comprises at least two or more regions of differing specific gravities. Preferably, at least one of the regions is higher than the target specific gravity and at least one of the regions is lower than the target specific gravity.
Preferably, the separator element comprises a toroid or a bellows, a foam or a float and a sinker or a ballast. The bellows comprises opposed first and second ends and a seal body extending between the ends. The outer diameter of the seal body is larger than the inner diameter of the tube for sealing engagement. Most preferably, the seal body has elastic properties.
Most preferably the float is securely mounted to the first end of the bellows and the ballast is securely mounted to the second end of the bellows.
Alternatively, the bellows comprises a first end that is a resealable septum and an open second end.
Preferably, the separator may be initially located at any position within the tube. Most preferably, the separator is held in position at the top of the tube by an interference fit between the seal body and the tube inner diameter.
Preferably, the separator has central passageway that extends from the first end through the seal body and to the second end of the bellows.
Preferably, the bellows has a specific gravity of about 0.8 to about 1.2. Most preferably, the bellows is made from an elastomer which has a 50% tensile modulus (YOUNGS) from about 100 psi to about 500 psi.
Desirably, the seal body may be comprised of any natural or synthetic elastomer or mixture thereof, that are inert to the fluid sample of interest and is flexible.
Preferably, the seal body comprises a qualitative stiffness, expressed as follows:
S
*
=
k
a
ρ
w
D
2
whereby S* is the non-dimensional stiffness coefficient, k is a force required to deflect the bellows a given length, a is the applied acceleration, D is the diameter of the seal body and &rgr;
w
is the density of water.
Desirably, the qualitative stiffness of the seal body is from about 0.00006 to about 190.
Preferably, the seal body may be subjected to a characteristic or radial deflection under an applied load, such as an axially applied load. The characteristic or radial deflection is defined as a change in length of the seal body relative to the change in cross section diameter of the seal body. Preferably, the seal body has a characteristic or radial deflection ratio of about 1.5 to about 3.5.
Preferably, the seal body when subjected to an applied load, such as centrifugation, to cause axial deformation of the seal body, the change in cross section diameter may be expressed as follows:
D
before
-
D
during
D
before
×
100
%
=
Δ
D
m
wherein &Dgr;D
m
is from about 5% to about 20%.
Therefore, a change in cross section diameter of the seal body is proportional to the undeflected cross section diameter of the seal body. Preferably, the proportion is from about 0.03 to about 0.20.
Desirably, the ballast is a substantially rigid moldable thermoplastic material such as polyvinyl chloride, polystyrene, polyethylene, polypropylene, polyethyleneterethalate, stainless steel, polyester and mixtures thereof that are inert to the fluid sample of interest. Most preferably, the ballast is a high density material. Preferably, the ballast is mounted around the second end of the bellows so as not to interfere with the central passageway of the separator. Mos
Karg Jeffrey
Lin Fu-Chung
Losada Robert J.
Miller Henry F.
Radziunas Jeffrey P.
Becton Dickinson and Company
Gakh Yelena
Thomas Nanette S.
Warden Jill
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